Spatial pattern analysis reveals multiple sources of organophosphorus flame retardants in coastal waters

Highlights

• Chinese coasts were found seriously polluted by organophosphorus flame retardants.

• Spatial pattern analysis was firstly used for pollution source identification.

• GBA PFRs pollutions were found correlated to local socio-economic indicators.

• Multiple human activities were proposed as sources of PFRs in GBA coastal waters.

Abstract

Organophosphorus flame retardants (PFRs) are a group of emerging contaminants which have been detected in worldwide waters. However, source of various PFRs in the large-scale area like coastal water environment have not been clearly revealed. In this study, fifteen PFRs in coast of Guangdong-Hong Kong-Macao Greater Bay area (GBA), China were investigated, and a method of spatial pattern analysis was firstly used for pollution source identification. Seawater samples from different segments of GBA coast were analyzed and thirteen PFRs were quantified with total concentrations ranging from 32.7 to 1032.7 ng L⁻¹. GBA coasts have been seriously polluted by PFRs. A hierarchical cluster analysis of the PFR concentrations in different GBA sites showed significant spatial distributions for different types of PFRs. A series of correlation analysis between PFRs distributions and spatial pattern of GBA socio-economic indicators were performed, and multiple sources including human settlement, wastewater, manufacture, construction industry, vehicles, and shipping transport were found to be correlated to PFRs pollutions in the coasts. This study indicates that spatial pattern analysis based on statistical analysis would be a promising method of analyzing environmental data and exploring pollution source in large-scale area.

Introduction

Organophosphorus flame retardants (PFRs) are a group of man-made industrial additives used as flame retardant and plasticizer, and have become by volume the most important organic FRs worldwide instead of brominated flame retardants in 2016 (McWilliams, 2018, van der Veen and de Boer, 2012, Bergman et al., 2012). However, PFRs are widespread organic pollutants and pose potential negative effects to biota and human beings; some PFRs have been proven to be neurotoxic, genotoxic, carcinogenic, etc. (Hou et al., 2016, Fu et al., 2020, Liu et al., 2021, Bekele et al., 2021). China was the largest single consumer with the use volume accounting for 26% of the global flame retardants market (data in 2016) (McWilliams, 2018). With the increasing population and fast-growing manufacturing industry in China, more PFRs are continuously released into natural waters and frequently detected (Shi et al., 2020). Guangdong-Hong Kong-Macao Greater Bay area (GBA) comprises Hong-Kong, Macao, and nine municipalities in the Pearl River Delta, China, and its development is a key strategic planning in China’s development blueprint (Hui et al., 2020, Zhou et al., 2018). GBA has the largest population, largest land area, highest manufacturing industry output values, and highest container throughput in bay areas all over the world (Hui et al., 2020). Previous studies have reported the pollution of various PFRs in Pearl River estuary in GBA, and the highest concentrations were up to 3.12 μg L⁻¹ (Wang et al., 2014). Hence, it is pertinent to study source of PFRs in GBA water environment, and the results may be helpful for identifying the contaminated industry and proceeding pollution mitigation in the future.

It has been reported that PFRs pollutions in urban rivers were highly related to the surrounding human activities (including social activities and industrial activities) (Gao et al., 2018, Gao et al., 2020, Zhang et al., 2019, Zhou et al., 2018). However, detail sources of PFRs in large-scale areas such as GBA coast have not been revealed clearly. PFRs have multiple usages in products (summarized in Fig. S1) and high mobility in surface water, which may lead to complex non-point source pollution (Chokwe et al., 2020). Spatial pattern analysis is focused on describing and analyzing pattern of data in space, and mainly applied in geographical and ecological analysis (Rosenberg and Anderson, 2011). This method may also be useful for discovering spatial pattern of environmental data and socio-economic data (Bierman et al., 2011). For instance, spatial pattern analysis can reflect relationship patterns of both the regional PFRs pollution and socio-economic indicators such as human activities (e.g., population density, wastewater volume, industrial output value). The combination between spatial pattern analysis and statistical analysis may be helpful for further identifying sources of PFRs pollution in the large-scale area.

The manufacturing industry in GBA is highly developed and almost covers all types of industries that using PFRs, while different GBA coastal cities have different layouts in society and economic (Hui et al., 2020, Zhou et al., 2018). In geography, there are multiple rivers that flow through different cities and flow into different segments of GBA coast (Hu and Li, 2009, Lai et al., 2015). Some researchers have reported that the river inflow is a critical factor to determine the coastal water in GBA (Lai et al., 2015). Hence, PFRs would also travel into the GBA coast by river input (Milliman, 2001). The geographical characteristic of multichannel river network in GBA would lead to different transport and spatial distributions of contaminants. As a result, the spatial pattern analysis of PFRs pollutions and socio-economic indicators is likely to explore the source of PFRs in GBA coastal areas.

In this study, spatial distributions of fifteen PFRs (Table S1) in GBA coasts were explored by the method of hierarchical cluster analysis (HCA). Multiple sources of the studied PFRs were discussed according to the PFR applications and correlation analysis of PFRs distribution and GBA social/industrial indicators.